All-polymer solar cells composed of binary blends of donor poly4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo1,2-b;4,5-b′dithiophene-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno3,4-bthiophene-)-2–6-diyl) (PBDTTT-CT ), and acceptor polymers naphthalene diimide-selenophene copolymer (PNDIS-HD) and perylene diimide-selenophene copolymer (PPDIS) had power conversion efficiencies (PCEs) of 1.3 and 2.1%, respectively. Ternary blend solar cells composed of PBDTTT-CTPNDIS-HD1−xPPDISx at 75 wt% PPDIS had a PCE of 3.2%, which is about a 50%–140% enhancement compared with the binary blend devices. Equality of the ternary blend short-circuit current to the sum of those of the binary blend devices, among other results, provided evidence of a parallel-like bulk heterojunction mechanism in the ternary blend solar cells. These results provide the first example of enhanced performance in ternary blend all-polymer solar cells.